Method of forming a terminal structure in a refractory base



June 30, 1970 K. F. SZOBONYA 3,517,437

METHOD OF FORMING A TERMINAL STRUCTURE IN A REFRACTORY BASE Original Filed Dec. 4, 1964 FIG. 2

FIG. 1

FIG. 5

FIG. 3

FIG. 6

INVENTOR.

KARL E SZOBONYA v 'rToRueY United States Patent 3 517 437 METHOD or FoRMrNo ATERMINAL STRUCTURE IN A REFRACTORY BASE Karl F. Szobonya, Orange, Calif., assignor to Beckman Instruments, Inc., a corporation of California Original application Dec. 4,1964, Ser. No. 416,074, now abandoned. Divided and this application June 19, 1967,

Ser. No. 662,223

Int. Cl. H01b 13/00; H05k 3/00 US. Cl. 29-624 Claims This invention relates to an improved terminal structure for electrical circuit components such as resistors, capacitors, inductors, and the like, employing a base or substrate formed of a refractory material.

This is a division of my copending application Ser. No. 416,074, filed Dec. 4, 1964, now abandoned, entitled Terminal Structure.

US. Pat. No. 3,134,085 issued May 19, 1964, entitled Variable Resistor with Terminal Structure and assigned to Beckrnan Instruments, Inc., the assignee of the present invention, discloses in accordance with a preferred form of the invention, a terminal structure comprising generally a headed pin formed from a malleable metal. The shank of the pin is serrated or grooved over a major portion of its length with a small cylindrical portion at its outer end for facilitating the insertion of the pin into the hole of the support base. The pin is forced into the hole so as to physically deform the serrations thereby rigidly retaining the pin within the hole wthout the use of cements or adhesives. A terminal means made of a conductive material is then applied to the exposed end of the pin to make contact with the resistance element.

While the terminal structure and method of mounting the structure described in the US. patent cited above provides numerous advantages over the prior art, certain deficienciesmay appear under certain circumstances. For example, when the terminal is made in the form of an elongated pin which protrudes a substantial distance from the lower surface of the base member, forces applied to the protruding end during handling may cause the pin to be loosened because the portion supported by the base member is only a small part of the over-all length of the pin. In addition, the existence of voids or spaces between and above the serrations may cause some of the conductive material, from which the terminating means is formed, to find its way into these spaces resulting in slight depressions or irregularities in the surface of the terminating means. Usually, this is not a problem since in most applications the terminating means does not participate in the mechanical operation of the device. For example, in the US. patent cited above, a rectilinear variable resistor is shown in which a wiper element slidingly engages the resistance element mounted on the base member. Since in the operation of this device the wiper element does not traverse the surfaces of the terminating means (designated by reference numeral 46 in the cited patent), depressions or irregularities in the surface of the terminating means do not affect the operation of the device. However, if, for example, the variable resistor is in the form of a circular structure and the wiper element is required to be continually rotated, the wiper element will traverse the surfaces of the terminating means each revolution. In this case, if surface roughness is present, a non-uniform wiper drag force results 3,517,437 Patented June 30, 1970 ice along with increasingly rapid wear of the wiper element contacts.

Accordingly, it is an object of the present invention to provide a method for atlixing same to a refractory base or substrate, which will result in a terminal mounting of superior strength and durability.

It is another object of the present invention to provide a method for mounting a terminal structure in a refrac tory base or substrate, which will not create surface irregularities or roughness in the terminating means overlaying the terminal structure.

According to a specific, exemplary embodiment of the present invention shown and described herein, there is provided a terminal pin serrated, knurled or otherwise roughened along a portion of its shank length. The serrated or knurled part of the terminal pin is inserted, under a slight interference fit, into a hole provided in a refractory base member which is in the green or unfired state. During the firing process, shrinkage of the base member causes the refractory material to fill the spaces between and above the serrations or knurlings, thus eliminating the spaces into which the conducting material forming the electrical element terminating means might otherwise flow and additionally providing an exceptionally secure and durable terminal mounting.

The novel features which are believed to be characteristic of the invention are set forth with particularity inthe appended claims. The invention itself however, together with further objects and advantages thereof, can best be understood by reference to the following description taken in connection with the accompanying drawings in which:

FIG. 1 is a partial side view of a terminal pin fabricated in accordance with the present invention;

FIG. 2 is an end view of the terminal pin of FIG. 1;

FIG. 3 is a partial top view, in section of the terminal pin of FIG. 1 in place in a refractory base member prior to firing;

FIG. 4 is a partial side view, in section, of the assem- Fbly' of FIG. 3 taken along plane 44;

FIG. 5 is a partial top view, in section, of the assembly of FIG. 3 after firing:

FIG. 6 is a partial side view, in section, of the assembly of FIG. 5 taken along plane 6-6; and,

FIG. 7 is a partial view, in section, of a variable resistance element employing the terminal structure of the present invention.

Referring now to the drawings, there is shown in FIGS. 1 and 2 a terminal pin 10, fabricated of a precious metal alloy such as gold-palladium, having a shaft or shank 12 of diameter A with axially-oriented protuberances or serrations 14, separated by adjoining depressions, projecting from the surface of the shank 12 near one of the ends of the shank. The outside diameter of the portion of the terminal pin having the serrations is designated by the letter C. The outer extremities of the serrations 14 may be brought to a sharp edge, as best shown in FIG. 2, to perrnit easy insertion of the terminal pin. However, the serrations 14 may be of any desired cross-sectional shape (when viewed end-wise as in FIG. 2) as for example, rectangular or semi-circular. Further, the serrations 14, instead of being parallel to the longitudinal axis of the terminalpin as depicted in FIG. 1, may be formed as a helical thread or portions of a helical thread to help prevent long-itudinal or axial displacement of the terminal pin once it is secured in place. As a substitute for the serrations 14, a cross-hatched or knurled pattern having an outside diameter C may be formed'in the surface of the terminal pin 10 or, as a further alternative, the surface of the pin may be merely roughened in a random pattern with projections of outside diameter 0.

Referring to FIGS. 3 and 4, the terminal pin 10 is inserted in a hole 16 of diameter B provided in a green or unfired substrate or base member 18 typically fashioned of a refractory material such as alumina or steatite. Insertion of the terminal pin 10 in hole 16 leaves voids or spaces 20, 22 and 24, respectively, between, over and under the serrations 14.

As best shown in FIG. 3, the diameter B of the hole 16 is slightly smaller than the outside diameter C of. the serrated portion of the terminal pin 10 so that a slight interference fit exists upon insertion of the terminal pin 10. The mechanical bond provided by the interference fit prevents the terminal pin 10 from being dislodged'or shifted during handling of the assembly. The relationships between the diameters A, B and C may be determined from the firing shrinkage characteristics of the refractory material from which a particular base member is made.

To compensate for the decrease in thickness of the base member 18 because of contraction during the firing process, the terminal pin 10 may be positioned in the hole 16 so that the top surface of the pin lies a small distance (designated by reference numeral 26 in FIG. 4) below the top surface of the base member 18. Since the firing shrinkage characteristics of refractory base materials may be determined, the distance 26 may be calculated beforehand, with the result that after the firing process, the top surfaces of the terminal pin 10 and base 18 will be substantially flush. In most instances, this eliminates the necessity of grinding down the top surface of either the terminal pin 10 or the base member 18 to bring these surfaces into alignment. 1

FIGS. 5 and 6 show the assembly of FIGS. 3 and after firing. Shrinkage of the refractory 'base member 18 and the corresponding shrinkage of the hole 16 causes the protuberances 14 to become imbedded in the side wall of the hole 16, the individual protuberances breaking up the continuity of the hole surface abutting the shank. The top surfaces of the terminal pin 10 and the base member 18 are now substantially flush. The refractory material occupying the spaces which existed prior to firing above, below and between the protruding serrations 14 prevents both axial and rotational displacement of the terminal pin 10.

FIG. 7 illustrates the application of the terminal structure of the present invention to a resistance device in which an electrical circuit component in the form of a resistance element 28 has been mounted in the form of a thin layer on the upper surface of refractory base member 18. The element 28 may be mounted after firing of the assembly comprising the base member 18 and the terminal pin 10. A terminating means, comprising a metallic layer 30 suitably bonded to the plane surface formed by the top surfaces of the base member 18 and the terminal pin 10, serves to electrically connect the end of the resistance element 28 with an external circuit through the terminal pin 10. Typically, the metallic layer 30 is silkscreened or applied as a paste and fired to yield a solid connection between the elements 28 and 10.

Although exemplary embodiments of the invention have been disclosed and discussed, it will be understood that other embodiments may be constructed employing the teachings of this invention. Further changes, modifications and substitutions which may be made without departing from the spirit of the invention will be apparent to those skilled in the art. Also, other applications of the invention are possible. By way of specific example, besides being useful as a terminal structure for resistors, capacitors, inductors and other circuit components mounted on a refractory base member, the concept disclosed may also be applied to feedthrough connections utilized in micromodules to connect circuit components which are afiixed to opposite sides of a substrate.

What is claimed is: 1. A method of mounting a terminal structure in a refractory base member which base member has top and bottom surfaces, said refractory base member being formed of a refractory material which shrinks upon the application of heat thereto, comprising the steps of:

forming, in said refractory base member, while said base member is in the unfired state, a hole of diameter B communicating with said top and bottom surfaces;

providing a conductive terminal pin of a length substantially greater than the distance between said top and bottom surfaces of said base member; forming on said terminal pin a shank having a diameter A which is smaller than said hole diameter B, and forming protuberances projecting from said shank of said terminal pin, said protuberances having an outer diameter C which is larger than said hole diameter B;

inserting said shank of said terminal pin in said hole, said protuberances having an interference fit with the sidewalls of the hole while said refractory base member is in the unfired state; and

heating and firing the assembly comprising said refractory base member and said terminal pin to cure said refractory base member and causing said base material to shrink around said protuberances.

2. The method of claim 1 in which said terminal pin is inserted so that an end of said terminal pin is substantially flush with said top surface of said base member.

3. The method of claim 2 which includes the step of grinding flush said top surface of said base member and said end of said terminal pin.

4. A method of mounting a terminal pin in a base member fabricated of a refractory material which shrinks when cured by the application of heat thereto, said base member having top and bottom surfaces comprising the steps of:

forming in said base member while said base member is in the uncured state, a hole of diameter B communicating with said top and bottom surfaces of said base member;

providing a conductive terminal pin and forming thereon a shank with outwardly projecting protuberances separated by adjoining depressions, said shank having an outer diameter C across said protuberances and an inner diameter A measured adjacent said depressions, said diameter A being less than said diameter B of said hole and said diameter C being greater than said diameter B of said hole;

inserting said shank of said terminal pin into said hole while said refractory material is in the uncured state, said terminal pin being positioned into said hole a distance such that said end of said terminal pin liesa small distance below said top surface of said base member, said protuberances causing an interference fit with the sidewalls of said hole; and

heating and firing the assembly comprising said base member and said terminal pin and causing said base material to shrink whereby all spaces around said terminal pin are substantially filled with said refractory material and said top surface of said base member is flush with said end of said terminal pin.

5. A method of mounting a terminal pin in a base member fabricated of refractory material which shrinks when cured by the application of heat thereto, said refractory base member having top and bottom surfaces, comprising the steps of:

forming, in said base member while said member is in the uncured state, a hole of diameter B communicating with said top and bottom surfaces of said base member;

providing a conductive terminal pin and forming adjacent one end thereof a shank with outwardly projecting protuberances separated by adjoining depressions, said shank having an outer diameter C measured across said protuberances and an inner diameter A measured adjacent said depressions, said diameter A being less than said diameter B of said hole and said diameter C being greater than said diameter B of said hole;

inserting said shank at said terminal pin into said hole while said refractory material is in the uncured state, said terminal pin being positioned a distance such that said end of said terminal pin lies substantially flush with said top surface of said base member, said protuberances being slightly embedded in the sidewalls of said hole and supporting said terminal pin therein; and

heating and firing the assembly comprising said base member and said terminal pin and causing said base material to shrink whereby the spaces around said protuberances on said shank of said terminal pin are substantially filled with said refractory material.

6. The method of claim 5 which includes the step of grinding flush said top surface of said base member and said end of said terminal pin.

References Cited UNITED STATES PATENTS FOREIGN PATENTS 1943 Germany.

CHARLIE T. MOON, Primary Examiner R. W. CHURCH, Assistant Examiner US. Cl. X.R. 

1. METHOD OF MOUNTING A TERMINAL STRUCTURE IN A REFRACTORY BASE MEMBER WHICH BASE MEMBER HAS TOP AND BOTTOM SURFACES, SAID REFRACTORY BASE MEMBER BEING FORMED OF A REFRACTORY MATERIAL WHICH SHRINKS UPON THE APPLICATION OF HEAT THERETO, COMPRISING THE STEPS OF: FORMING, IN SAID REFRACTORY BASE MEMBER, WHILE SAID BASE MEMBER IS IN THE UNFIRED STATE, A HOLE OF A DIAMETER B COMMUNICATING WITH SAID TOP AND BOTTOM SURFACES; PROVIDING A CONDUCTIVE TERMINAL PIN OF A LENGTH SUBSTANTIALLY GREATER THAN THE DISTANCE BETWEEN SAID TOP AND BOTTOM SURFACES OF SAID BASE MEMBER; FORMING ON SAID TERMINAL PIN A SHANK HAVING A DIAMETER A WHICH IS SMALLER THAN SAID HOLE DIAMETER B, AND FORMING PROTUBERANCES PROJECING FROM SAID SHANK OF SAID TERMINAL PIN, SAID PROTUBERANCES HAVING AN OUTER DIAMETER C WHICH IS LARGER THAN SAID HOLE DIAMETER B; INSERTING SAID SHANK OF SAID TERMINAL PIN IN SAID HOLE, SAID PROTURBERANCES HAVING AN INTERFERENCE FIT WITH THE SIDEWALLS OF THE HOLE WHILE SAID REFRACTORY BASE MEMBER IS IN THE UNFIRED STATE; AND HEATING AND FIRING THE ASSEMBLY COMPRISING SAID REFRACTORY BASE MEMBER AND SAID TERMINAL PIN TO CURE SAID REFRACTORY BASE MEMBER AND CAUSING SAID BASE MATERIAL TO SHRINK AROUND SAID PROTUBERANCES. 